This application claims the priority of German Patent Document 100 07 382.4, filed Feb. 18, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an air spring system for a two axle motor vehicle with a compressed air source and control valves, which are assigned to the individual motor vehicle wheels and by means of which the respective vehicle wheel-air springs can be selectively connected to a compressed air supply line, connected to the compressed air source. Furthermore, the air springs of the vehicle front axle and those of the vehicle rear axle have their own compressed air line branches. For the technical environment reference is made to the European Patent Document EP 0 791 492 A1, as an example.
Air spring systems differ from solely mechanically suspended wheel suspensions owing to their higher flexibility or greater variability. Thus, in the case of a complete air spring system for a two or more axle motor vehicle the height of the vehicle body compared to the ground and thus the ground clearance of the motor vehicle can be varied. Usually so-called open air spring systems are used, where in the case of the vehicle body being lowered from a raised position, the air mass, to be bled from the air springs for said body, is bled over a so-called ventilation line into the atmosphere, i.e. into the environment. Since this lowering is supposed to take place within a relatively short period of time, the document cited in the introductory part of the specification proposes circumventing in a bypass the so-called control valves, which in themselves constitute a flow resistance, during the lowering procedure. To fill the individual motor vehicle wheel air springs, in contrast, the compressed air that is conveyed from the compressor and, in addition, is usually taken from a storage volume, is guided over or through these control valves.
Among other things, owing to the non-uniform distribution of the motor vehicle body weight, the so-called static air pressure in the air springs, assigned to the vehicle front axle, can differ from that of the rear axle air springs. If at this point both the air springs of the front axle of the motor vehicle and those of the vehicle rear axle are supposed to be filled with additional air, starting from a lowered vehicle body level, in order to convey the vehicle body into a raised level, the front axle air springs and the rear axle air springs were filled at different rates owing to the said pressure differential so that while the vehicle body was pumped up, so to speak, said vehicle body would be tilted relative to the horizontal line.
For example, the amount of static air pressure in the air springs of the rear axle would be higher than that of the front axle. Then, in lifting or pumping up the vehicle body, it would be tilted so as to fall off in the direction of the rear. The situation is the same when lowering the vehicle body as a result of a partial removal of air from the air springs, since then the rear air springs would be emptied due to the positive pressure gradient relative to the front air springs. In the extreme case the front air springs could even be filled with air from the rear air springs.
An object of the present invention is to provide a remedy for the problem described above.
The solution to this problem according to the invention is characterized by the fact that the flow cross section of the is compressed air line branch(es), which are assigned to the air springs of the vehicle front axle, differs at least by segments from that of the compressed air line branch(es), assigned to the air springs of the vehicle rear axle. Furthermore, the line branch of one of the two axles is designed in such a manner that its flow cross section during compressed air feed into the assigned air springs differs at least by segments from the flow cross section during compressed air bleeding from the assigned air springs.
An especially simple and, therefore, advantageous air spring system of the invention is obtained when that line branch, whose flow cross section during compressed air feed differs from that during compressed air bleeding, comprises parallel connected subbranches with flow cross sections that differ at least by segments; and at least one of the subbranches exhibits a suitably arranged non-return valve, which releases this subbranch only in one direction of flow.
The invention is explained in detail with the aid of two preferred embodiments, where reference is made explicitly to the fact that the invention is not restricted to these embodiments. Important are rather the features, which are disclosed in the patent claims and which are described in greater detail below.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.